<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="./vue.js"></script>
</head>
<body>
<button onclick="fn()">点我</button>
<div id="root">
  <p>{{a}}</p>
  <p>{{b}}</p>
  <p>{{c}}</p>
  <p>{{d}}</p>
</div>
</body>
<script>
  const data={
    a:1,
    b:2,
    c:3,
    d:4
  }
  vm= new Vue({
    el: '#root',
    data
  });

  function fn(){
    vm.$data.a=100;
    console.log(data);
  }
  console.log(vm.$data===data);  //true

</script>
</html>